► Some commercial copper chromite catalysts have been tested in ethanol dehydrogenation. ► A satisfactory activity and very high selectivity and good stability to sintering has been obtained for one ...of the proven catalysts. ► The best catalyst is a dispersed Cu catalyst, supported on alumina containing Cu chromite and BaCrO
4. ► Optimal conditions for high selectivities are:
T
=
240
°C,
P
=
20 bars and ethanol contact time (100
g
h
mol
−1). ► Pure hydrogen (exempt of CO) is obtained as by-product.
In the recent years, the interest in the ethanol production from renewable natural sources, as a possible alternative energy vector, has strongly grown in the world. The low-cost ethanol availability has also favored the study of the production of different chemicals such as ethylene, ethyl ether, acetaldehyde and ethyl acetate starting from ethanol as raw material. In this paper, ethanol dehydrogenation to ethyl acetate, in one step reaction, has been studied by using three different commercial copper based catalysts. The reaction has been conducted in a conventional packed bed tubular reactor, by exploring a temperature range of 200–260
°C and a pressure range of 10–30 bars. The best results have been found by using a commercial copper/copper chromite catalyst, supported on alumina and containing barium chromite as promoter, operating at 220–240
°C, 20 bars and 98
g
h
mol
−1 of ethanol contact time. In these conditions, a conversion of 65% with a selectivity to ethyl acetate of 98–99% has been obtained. However, the effect of temperature, pressure and ethanol contact time on both conversion and selectivity to ethyl acetate has been investigated. Moreover, the best catalyst has also shown a good stability to deactivation. For these reasons, the behavior of this catalyst has been subjected to a deeper investigation. The obtained results have been discussed on the basis of a reliable reaction scheme and mechanism. At last, a simplified scheme of a possible process is reported.
The gas separation and gas barrier properties of nanocomposite membrane made of low-density polyethylene (LDPE) with dispersed graphite nanoplatelets (GNPs) were studied by gas phase permeation ...technique. Structural and morphological analyses indicate that in nanocomposites prepared by film blowing technology: (i) the GNPs are iso-oriented with the platelet surface parallel to the membrane surface and (ii) the GNPs inclusion does not change the crystalline fraction of the polymeric matrix nor the size of the LDPE crystallites. The H2, N2, and CO2 transport through the nanocomposite membrane was investigated in samples with nominal GNPs content of 5wt%. The GNPs inclusion reduces the permeability by approximately a factor two compared to that of the pure LDPE membrane for all the examined gases without relevant changes in the gas selectivity properties. Gas transport through the nanocomposite membrane obeys to the solution–diffusion mechanism and shows, for the examined gases, the same value of activation energy for permeation as in the pure LDPE sample. The gas barrier properties of the nanocomposite were compared with those predicted by phenomenological models. The reduced permeability cannot be explained assuming that gas molecules have to cross a tortuous migration path in the polymeric matrix but was instead attributed to the formation of rigidified polymer layers around the GNPs filler particles.
•Nanocomposites of iso-oriented graphite nanoplatelets in polyethylene matrix.•Gas transport through nanocomposites studied by gas-phase permeation techniques.•Gas transport by solution–diffusion mechanism as in pure polyethylene.•Nanocomposites are gas barrier, no changes in gas separation properties.•Formation of rigidified polymer layers at the filler–matrix interface.
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► A kinetic study of the ethanol dehydrogenation to ethyl acetate. ► Cu/CuCr2O4 as catalyst supported on Al2O3 promoted with BaO–Cr2O3. ► A Langmuir–Hinshelwood–Hougen–Watson kinetic ...model resulted the best to interpret all the performed kinetic runs. ► A reliable mechanism is suggested and discussed.
A kinetic study of the ethanol dehydrogenation to ethyl acetate on a copper/copper-chromite catalyst has been performed. The used catalyst, in cylindrical pellets, contained also alumina as a support and barium chromate as a promoter. Support and promoter have the effect of increasing the activity, the selectivity and the stability of the catalyst, as shown in a previous work. The kinetic runs were carried out in a packed bed tubular reactor, alternatively filled with 2 or 50g of catalyst, approximately isothermal, by feeding pure ethanol together with a mixture of nitrogen and hydrogen as carrier gas. Kinetic runs have been made by changing the temperature, in the range of 200–260°C, the pressure between 10 and 30bar and the space time from 1 to 100ghmol−1. We have verified, at first, that inter-phase and intra-phase mass transfer limitations were negligible in the adopted conditions. Then, a Langmuir–Hinshelwood–Hougen–Watson kinetic model has been used for interpreting all the experimental data collected. This model corresponds to a mechanism in which the first step is the dissociative adsorption of ethanol on the surface, giving an adsorbed ethoxy group. Then, two other consecutive steps give place to respectively acetaldehyde as intermediate and ethyl acetate. This kinetic model allows a satisfactory fitting of all the performed experimental runs with a standard error below 15% for the runs performed with 2g of catalyst and less than 12% for the runs made with 50g of catalyst.
The mechanical properties of GNP/LDPE nanocomposites (graphite nanoplatelets/low density polyethylene) have been investigated, in order to establish the effect of nanoscale reinforcement within the ...polymer matrix. Results show that the presence of the filler does not involve a change in the microscopic structure of the polymer. However, on a macroscopic scale, GNPs limit the mobility of the polymer chains, resulting in an increase in stiffness for the final composite. Orientation of GNPs within the LDPE matrix is also an important issue that affects mechanical properties and it has been evaluated by testing nanocomposites made by different manufacturing techniques (compression moulding and blown extrusion). The comparison between the experimental data and the Halpin-Tsai model shows that the orientation of GNPs due to the extrusion process leads to values of tensile modulus higher than that obtained with the randomly oriented disposition resulting from the compression moulding technique.
Pd(0) is able to catalyze oxygen-involving reactions because of its capability to convert molecular oxygen to the very reactive atomic form. Consequently, the embedding of a little amount of Pd(0) ...clusters in polymeric phases can be technologically exploited to enhance the incineration kinetic of these polymers. The effect of nanostructuration on the Pd(0) catalytic activity in the polymer incineration reaction has been studied using poly(
N
-vinyl-2-pyrrolidone) (
Mw
¯
= 10,000 gmol
−1
) as polymeric model system. A change in the PVP incineration kinetic mechanism with significant increase in the reaction rate was experimentally found. The kinetic of the Pd(0)-catalyzed combustion has been studied by isothermal thermogravimetric analysis. After a short induction time, the combustion in presence of Pd(0) clusters shifted to a zero-order kinetic from a second-order kinetic control, which is operative in pure PVP combustion reaction. In addition, the activation energy resulted much lowered compared to the pure PVP incineration case (from 300 to 260 kJ/mol).
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► Grafted VOx on TiO2/SiO2 catalysts for selective photocatalytic oxidation of ethanol to acetaldehyde. ► Ethanol conversion decreased by increasing TiO2 loading. ► Further ...enhancement of acetaldehyde yield by the highly active V species. ► In presence of phosphors, photoactivity increased with the increase of ethanol inlet concentration.
In this work gas phase photocatalytic selective oxidation of ethanol to acetaldehyde was studied with directly fluidizable photocatalysts made of grafted VOx on titania/silica in presence of phosphors as light carriers to test their performances in the photocatalytic system. The presence of VOx species anchored on TiO2/SiO2 enhanced ethanol conversion up to 66%, with acetaldehyde selectivity higher than 99%. The performances of V-based sample at 11wt% of TiO2 supported on fluidizable support were higher than those evaluated when nano-TiO2 powder is used as support. Moreover, the photocatalytic conversion of ethanol was further increased in presence of phosphors as light carriers. From the obtained results, it is concluded that by preparing VOx based catalyst through grafting method allows a dramatic enhance in the productivity of acetaldehyde, even when the concentration level of alcohol at photoreactor inlet is increased.
Objectives
To evaluate the serum symmetric dimethylarginine (SDMA) and serum creatinine concentrations in a population of hypothyroid dogs at the time of diagnosis and after treatment.
Materials and ...Methods
Serum SDMA and serum creatinine were measured in serum samples of 24 healthy dogs and 24 hypothyroid dogs, at the time of diagnosis (T0) and after supplementation with levothyroxine (T1).
Results
The mean SDMA concentrations (reference intervals RI <18 μg/dL and <14 μg/dL depending on the source) were 11.7 ± 3.5 μg/dL, 13.8 ± 3.1 μg/dL and 11.83 ± 2.87 μg/dL in healthy dogs, and in the hypothyroid dogs at T0 and T1, respectively. The SDMA concentrations were higher in the hypothyroid dogs at T0 in comparison with the healthy dogs. Of the hypothyroid dogs, 1 out of 24 had an SDMA concentration above 18 μg/dL and 12 out of 24 above 14 μg/dL at T0. At T1, none of the hypothyroid dogs had SDMA concentrations above 18 μg/dL and two of them had SDMA concentrations above 14 μg/dL. The serum creatinine concentration was higher in the hypothyroid dogs at T0 as compared to the healthy dogs. At T0, 8 out of 24 hypothyroid dogs had serum creatinine concentrations above the RI (>1.4 mg/dL). In all but one dog, serum creatinine normalised after treatment.
Clinical Significance
The SDMA and serum creatinine concentrations were higher in hypothyroid dogs at diagnosis as compared to healthy dogs. Serum creatinine concentrations were increased in one‐third of the hypothyroid dogs and in the majority of cases normalised after levothyroxine supplementation. SDMA concentrations were rarely above the upper limit of the RI when the higest (<18 μg/dL) cut‐off was employed. The diagnostic accuracy of SDMA in dogs with thyroid dysfunction requires additional evaluation.
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